While the present invention can be effectively used in a plurality of paper handling or marking systems, it will be described for clarity as used in electrostatic marking systems such as electrophotography. In an electrostatographic reproducing apparatus commonly used today, a photoconductive insulating member may be charged to a negative potential, thereafter exposed to a light image of an original document to be reproduced. The exposure discharges the photoconductive insulating surface in exposed or background areas and creates an electrostatic latent image on the member which corresponds to the image areas contained within the original document. Subsequently, the electrostatic latent image on the photoconductive insulating surface is made visible by developing the image with a developing powder referred to in the art as toner. During development, the toner particles are attracted from the carrier particles by the charge pattern of the image areas on the photoconductive insulating area to form a powder image on the photoconductive insulating area to form a powder image on the photoconductive area. This image may be subsequently transferred or marked onto a support surface such as copy paper to which it may be permanently affixed by heating or by the application of pressure. Following transfer of the toner image or marking, the copy paper may be removed from the system by a user or may be automatically forwarded to a finishing station where the copies may be collected, compiled and stapled and formed into books, pamphlets or other sets.
As above noted, there are many marking systems that transport paper or other media after the paper is marked in marking step or steps. These marking systems could include electrostatic marking systems, non-electrostatic marking systems and printers or any other system where paper or other flexible media or receiving sheets are transported internally to an output device such as a finisher and compiler station or stations. These devices include those used for collecting or gathering printed sheets so they may be formed into sets such as books, pamphlets, forms, sales literature, instruction books and manuals and the like.
These electrostatic marking systems have finisher and compilers located at a site after the receiving sheets (paper) have been marked with a toner. A finisher is generally defined as an output device that has various post printer functions or options such as hole punching, corner stapling, edge stapling, sheet and set stacking, letter or tri-folding, Z-folding, Bi-folding, signature booklet making, set binding (including thermal, tape and perfect binding), trimming, post process sheet insertion, saddle stitching and others. In today's marketplace stacking and stitching finishers for cut sheet digital printers or marking systems typically do not exceed throughput rates greater than about 160-180 prints per minute (ppm) for letter size substrates. These rates are typically further reduced when handling small stitched set sizes (i.e. 2-4 sheets). With the emphasis today on digital marking products capable of ever increasing throughput, the need for finishing devices capable of handling these higher speeds for both stacking and stitching for all set sizes is important.
Today, there is no reliable cut sheet digital stacking and stitching finisher module that is capable of handling prints per minute of up to 360 ppm. As throughputs of marking systems become higher and higher, there will be a need for a finisher module capable of handling cut marked sheet substrates for both stacking and stitching at productivity rates of upwards of 200 ppm and greater and at the same time not being large and bulky so as to take up valuable space at the finisher station. Also, a module capable of providing both stapled and non-stapled prints would enhance the versatility and adaptability of such a finisher module.
Disk or disc-stacking apparatus and sheet inverters are well known in the art such as disclosed in Xerox U.S. Pat. Nos. 5,188,353; 5,261,655; 5,409,202; 5,476,256; 5,570,172; 5,842,695; 6,443,450 and 6,575,461. The disclosures of these Xerox Patents are incorporated by reference into this disclosure.